This invention relates generally to incinerator grate plates. More particularly, the present invention relates to liquid-cooled incinerator grate plates.
For burning solid materials, especially at trash incinerators, furnaces are used which employ so-called feed grates capable of accepting and feeding the material to be incinerated with a forward motion. These feed grates are composed of bars or plates some of which are mounted in stationary position while groups of others move back and forth, i.e. alternating toward and away from the feed port.
The grate as a whole commonly consists of multiple bars or plates arranged side by side and one behind the other. Slotted nozzles in the bars or plates allow combustion air to flow to the material to be incinerated.
During the incineration process the burning solids cause the grate bars or plates to heat up considerably. The combustion air flowing through the slots, which is usually preheated or limited in quantity for reasons of combustion properties, can provide very little cooling at best. Uncooled grate bars or plates thus reach relatively high temperatures, which tends to cause strong chemical corrosion and physical wear, an obviously undesirable factor.
Strongly heated grate plates expand during operation. Allowing for such expansion requires a certain amount of `play`. That in turn can create gaps between the grate plates which admit air into the incineration chamber. This air flow is uncontrolled which is again an undesirable factor. Excessive amounts of air also have a negative effect on the combustion process. Smaller particles can drop through the gaps and collect underneath the grate, yet another undesirable factor.
For these two underlying reasons it is desirable to cool grate plates during operation, i.e. to keep them at a constant temperature. To that end, German patent DE 196 13 507 C1 proposes a grate plate that extends across the entire path of the grate. The grate plate incorporates numerous parallel cooling channels which run in the longitudinal direction and lead to manifolds at the end.
This type of grate plate permits effective cooling without requiring an allowance for expansion gaps which would admit an undesirable air flow. Of course, extending across the entire width of the grate, the plate becomes relatively large.
EP 0621449 B1 describes a grate plate with a serpentine cooling channel which latter runs along the horizontal axis of the grate plate and !,thus perpendicular to the feed motion. Due to the meandering course of the cooling channel some sections of the channel extend in the longitudinal direction.
A cooling-water intake on one side and an outlet for the warmed-up cooling water on the other side of the grate plate produces a thermal gradient which can cause different degrees of expansion on the two sides of the grate. Different expansion coefficients in turn can cause the plate to warp and to produce cracks which are substantially wider than the thermal expansion itself. To minimize this effect, a relatively strong coolant flow is necessary. The coolant cannot be allowed to warm up much if a warping or distortion of the grate plate due to thermal expansion differentials is to be avoided. Otherwise, gaps could form between adjoining grate plates, allowing uncontrolled air to enter the combustion chamber and debris to fall through these gaps.